Field of the Invention
The present invention relates to a method for compensating for the rotational irregularities of an internal combustion engine of a drive train of a hybrid vehicle, wherein an electric motor of the drive train is connected via a drive shaft to the drive wheels and via an engine shaft to the internal combustion engine, which introduces rotational irregularities into the drive train, and the electric motor is controlled by a drive controller which supplies a controlling torque to the electric motor.
The Prior Art
A known drive train concept of a modern hybrid vehicle includes an electric motor which drives the drive wheels of the vehicle, optionally a transmission, a differential gear and side shafts, via a drive shaft. The electric motor is additionally connected to an internal combustion engine via a coupling and connecting shaft in order to increase the cruising range of the hybrid vehicle. For this purpose, smaller internal combustion engines are used, e.g., 2- or 3-cylinder engines, since the internal combustion engine is only used for supporting the electric motor. However, due to the combustion impacts, the internal combustion engine has a cyclically varying torque, resulting in rotational irregularities at the drive (or flywheel) of the internal combustion engine. These rotational irregularities propagate via the electric machine into the drive train and are sensed there as vibrations, which reduces the driving comfort of the hybrid vehicle.
Thus, control strategies which try to compensate for these rotational irregularities in the drive train have already become known. For example, a control that compensates for the rotational irregularity by means of a so-called Harmonic Oriented Control (HOC) has been introduced as part of the lecture “Efficient E-vehicle drive with the compact CEA concept—Combustion Engine Assist”, C. Beidl et al., 7th MTZ symposium The drive system of tomorrow, January 24 and 25, 2012, Wolfsburg. Here, analogously to the field-oriented control of electric motors, a Park's transformation of the torsional vibrations into a coordinate system rotating synchronously with the frequency of the vibration is performed. In the course of this, accelerations involved in the vibration are compensated for the new coordinate system by means of two PI controllers so that after the inverse transformation, a compensation portion of the target torque to be predefined is obtained, which is used to correct the target torque of the speed controller of the electric motor.
A similar concept can be found in WO 2012/156258 A2, wherein here the compensation is carried out prior to the field-oriented control of the electric motor.
Both methods have in common that relatively high computing effort is required for performing the transformations, which also results in a correspondingly powerful computing unit for the implementation in the vehicle.
DE 10 2009 047 116 A1 and DE 199 39 250 A1 describe methods for compensating a rotational irregularity in a drive train from an internal combustion engine and an electric motor, in which first the rotational irregularity is determined, and the electric motor is controlled to counteract the rotational irregularity. However, due to the system delays and the disadvantages of the controller, this is only possible up to a certain degree of the dynamic of the rotational irregularity.
It therefore was an object of the present invention to propose an alternative control of an electric motor of such a drive train of a hybrid vehicle, which can be implemented and carried out in a particularly simple manner.